1. Field of the Invention
The present invention pertains to respiratory patient interface devices and, in particular, to a method of providing a semi-custom patient interface device.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheal tube in their esophagus. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation. It is also known to deliver positive airway pressure (PAP) therapy to treat certain medical disorders, the most notable of which is obstructive sleep apnea (OSA). Known PAP therapies include continuous positive airway pressure (CPAP), wherein a constant positive pressure is provided to the airway of the patient in order to splint open the patient's airway, and variable airway pressure, wherein the pressure provided to the airway of the patient is varied with the patient's respiratory cycle, and auto-titrating pressures, wherein the pressure varies with the condition of the patient (e.g., snoring, apneas, hypopneas, etc.) or with the condition of the therapy system (e.g., large leaks). Such therapies are typically provided to the patient at night while the patient is sleeping.
Non-invasive ventilation and pressure support therapies as just described involve the placement of a patient interface device including a mask component having a soft, flexible cushion on the face of a patient. The mask component may be, without limitation, a nasal mask that covers the patient's nose, a nasal cushion that rests beneath the patient's nose (such as a “pillows” style nasal cushion having nasal prongs that are received within the patient's nares or a “cradle” style nasal cushion that rests beneath and covers the patient's nares), a nasal/oral mask that covers the nose and mouth, or a total face mask that covers the patient's face. Such patient interface devices may also employ other patient contacting components, such as forehead supports, cheek pads and chin pads. The patient interface device is connected to a gas delivery tube or conduit and interfaces the ventilator or pressure support device with the airway of the patient, so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient.
The mask component of a patient interface device has a certain amount of leak designed into it for allowing exhaled gas to leave the system. This designed-in leak is known as intentional or exhalation leak and is the leak needed to remove exhaled gases from the system. Residual leak is the leak that is not designed into the mask but is still present, often due to a poor fit. Traditionally, the dimensions and contours of the patient interface device were based on a generic model. That is, the patient interface device was sized and shaped to fit on a user with broadly average facial features. One advantage to such generic patient interface device is that by being structured to fit onto a variety of faces, the generic patient interface device would also provide an adequate fit for a single user regardless of that user's expression. While this construction allows for mass production of patient interface devices, the patient interface devices typically did not fit any one person precisely. When the patient interface device does not fit a user precisely, there is an increased chance that the patient interface device will allow fluid, typically pressurized air, to leak. Further, a patient interface device that does not fit a user correctly may be uncomfortable. There have been at least two attempts to overcome these problems.
Initially, patient interface devices were adapted to multiple generic models. That is, there was a generic female patient interface device, a generic child patient interface device, etc. While these patient interface devices allowed for a better fit than the broadly generic model, the problems persisted because the patient interface devices still did not fit any one person precisely. As three-dimensional scanning techniques improved and custom fabrication became less expensive, custom patient interface devices could be fabricated. Ironically, custom patient interface devices suffered from some of the same problems as the patient interface devices that were based on a generic model, i.e. a custom patient interface device often provided a bad fit. This was likely because the three-dimensional scanning techniques typically provided a snapshot of the user's face at a single moment, i.e. with a single facial expression. This, in turn, created at least two similar problems when creating custom patient interface devices.
First, if the user had a particular facial expression, such as a smile or frown, when the scan was being made, the custom patient interface device would be structured to fit the user when the user had the same expression. Thus, users were typically advised to maintain a “neutral expression” during the scan. The second problem was, even if a user maintained a neutral expression during the scan, the resulting parameters that were measured were based exclusively on the user's face at a single moment in time. While a custom patient interface device based on a scan of a neutral expression typically fit better in most instances than would a custom patient interface device based on a scan of a particular expression, the custom patient interface device was still structured to fit the user's single expression. That is, if during use of the custom patient interface device, the user changed their expression from the neutral expression, the custom measurements were no longer accurate and the custom patient interface device did not provide a precise fit.
Thus, a generic patient interface device provided a fit that was generally acceptable to a variety of face sizes and shapes, but not precise to any specific one. Conversely, a custom patient interface device provided a fit that was precise for a user so long as the user's face maintained the expression that was captured in the scan upon which the custom patient interface device was based.